Project Summary B-cells and antibodies are a critical interface between the innate and adaptive immune systems since they have both natural and acquired recognition of microbial antigens. However, the antibodies that naturally bind microbial antigens frequently also react with self-antigens and, in health, these autoreactive B-cells have to be stringently regulated to prevent autoimmunity. Recent evidence from our laboratory has previously demonstrated that B-cells, plasmablasts and self-reactive autoantibodies against DNA and the basement membrane are strikingly elevated in nasal polyp tissue especially in patients with severe disease. Furthermore, we find that highly specific markers for antibody-mediated complement activation like C4d and C1rs-inh are found at high levels within nasal polyp tissue suggesting these antibodies are activating potent pro- inflammatory immune cascades. Our central hypotheses for the proposed work are: 1) that the these autoantibodies are cross-reactive with natural antibodies that bind microbial antigens, 2) that the levels of autoreactive antibodies may predict nasal polyp recurrence and 3) that the autoreactive B-cells in nasal polyps may represent a pathogenic manifestation of a subtype of B-cells called B-1 cells that have been well characterized in mice but remain enigmatic in humans. In the highly translational research proposed, we will leverage the Principal Investigator?s expertise as a surgeon-scientist whose clinical interests focus on CRS patients with his research interests in mucosal immunity. Specific aims in the experiments will: (1) identify the specific tissue antigens that are recognized by nasal polyp derived antibodies and evaluate their potential to cross-react with microbial proteins and activate complement; (2) comprehensively analyze samples collected from a prospective observational trial of nasal polyp recurrence after sinus surgery for autoantibodies and complement. Survival analysis will then be used to evaluate the biomarkers that provide significant prognostic information; and (3) isolate the cells producing autoantibodies to identify lineage markers, conduct analysis of antibody structural diversity and generate monoclonal autoantibodies from these cells for future studies. If successful, these studies will firmly establish a novel pathogenic mechanism in a debilitating upper airway disease, validate novel biomarkers of prognostic value, and discover fundamental features of human mucosal B-cells.